<!DOCTYPE html>
<html lang="zh-CN">
<head>
  <meta charset="UTF-8">
  <meta name="author" content="wangbo">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .item{
      box-sizing: border-box;
      height: 200px;
      float: left;
      
      width:calc(100%/3);
      border: 1px solid #ccc;
      
    }
  </style>
</head>
<body>
  <div class="list">
    <div class="item">我是div1</div>
    <div class="item">我是div2</div>
    <div class="item">我是div3</div>
    <div class="item">我是div4</div>
    <div class="item">我是div5</div>
    <div class="item">我是div6</div>
    <div class="item">我是div7</div>
    <div class="item">我是div8</div>
    <div class="item">我是div9</div>
  </div>
</body>
</html>